She's not going to meet him for closure. What the heck is that supposed to mean, anyway? They DIVORCED. He ignored her for 20 years. How much more closed can a relationship be than that?

She thinks she's in love with him. She is confused.
Expose the affair. This is your single strongest tool in ending it. Your marriage cannot recover while she is in an affair.

Don't tell her your plans, don't make threats. Just get a list of people and their phone numbers and start making calls. Exposure targets:
OM's wife
WW's parents
Friends that you know are pro-marriage
Clergy if you are religious
Your step daughter
Your daughter

Exposure is not done out of malice. It is done out of love. It goes like this:
WW is having an affair with OM. I am devastated, of course, but I want more than anything to reconcile with my wife and build a new and better marriage with her. I'd greatly appreciate your support and I welcome any advice you might have.

Expose to everyone on the same day. Go nuclear with it.
Your WW will be FURIOUS. She will tell you that she hates you, she wants a divorce, you have destroyed her trust in you (hahahaha), that any chance the marriage might have had is gone now, that you have shown your true colors, blah blah blah.

The backlash is because she won't be happy having her fantasy world exposed to the light of day. And it IS a fantasy world. If it were truly so great and wonderful, she wouldn't care who knew.